The subject matter described herein relates generally to wind turbines and, more particularly, to a method and apparatus for controlling a wind turbine.
Generally, a wind turbine includes a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on a base that includes a truss or tubular tower.
Some wind turbine configurations include double-fed induction generators (DFIGs). Such configurations may also include power converters that are used to convert a frequency of generated electric power to a frequency substantially similar to a utility grid frequency. Moreover, such converters, in conjunction with the DFIG, also transmit electric power between the utility grid and the generator. A wound rotor of the DFIG also receives excitation power from one of the connections to the utility grid.
Electric utility grids are often designed to operate at specified frequencies, or within specified frequency ranges. Certain events, such as an overproduction of power, may increase the utility grid frequency above a predefined frequency limit (also known as overfrequency conditions). If not corrected, such overfrequency conditions may cause damage to utility grid components and/or to loads that are coupled to the utility grid. At least some known power systems reduce a power output of one or more generators in response to overfrequency conditions. However, such reduction of power may be slow, and existing overproduction of power may persist while the generator reduces its power output.